A grain product is any food made from wheat, rice, oats, cornmeal, barley or another cereal grain. Grains are divided into two subgroups: whole grains and refined grains. Whole grains contain the entire grain kernel — the bran, germ and endosperm. Refined grains have been milled, a process that removes the bran and germ. This is done to give grains a finer texture and improve their shelf life, but it also removes dietary fiber, iron and many B vitamins.
Government dietary guidelines advise making half of your grain intake whole grains. For example, choose 100% whole-wheat bread instead of white bread, and brown rice instead of white rice.
— Source: National Institute of Diabetes and Digestive and Kidney Diseases